One important aim in the development of power semiconductor components is to produce components with as high a blocking capability as possible, which would nevertheless have a low on-state resistance and have switching losses which are as low as possible at the same time.
One possible way to reduce the on-state resistance of a power semiconductor component for a given blocking capability is to use the compensation principle, which is described by way of example in U.S. Pat. No. 4,754,310 (Coe), U.S. Pat. No. 5,216,275 A1 (Chen), U.S. Pat. No. 5,438,215 or DE 43 09 764 C2 (Tihanyi). The compensation principle envisages the provision of semiconductor zones with complementary doping to one another in the drift zone of a power semiconductor component, which semiconductor zones mutually clear out charge carriers in the blocking state. However, as the magnitudes of the structure widths are reduced to an ever greater extent, the compensation principle is reaching its limits, since the drift zone has to have a minimum width in the direction transverse with respect to the current flow direction for correct operation.
The on-state resistance of a power semiconductor component can also be reduced by providing heavier doping in the drift zone and by arranging a field electrode adjacent to the drift path in the component, which field electrode in the case of a component which is driven such that it is in the blocking state produces an opposing charge to the charge which is present in the drift zone and results from the doping. This opposing charge compensates for charge carriers in the drift zone, so that heavier doping is possible in the drift zone, and thus a lower on-state resistance, for a given blocking voltage, or a higher blocking voltage is possible for a given doping. Components such as these are described, for example, in U.S. Pat. No. 4,903,189 (Ngo), U.S. Pat. No. 4,941,026 (Temple), U.S. Pat. No. 6,555,873 B2 (Disney), U.S. Pat. No. 6,717,230 B2 (Kocon), U.S. Pat. No. 6,853,033 B2 (Liang). One problem in this case is that the voltages which can occur across the isolation layer between the drift zone and the field electrode when the component is in the blocking state are high in some circumstances, so that this isolation layer must be appropriately thick in order to have an adequate withstand voltage. However, this adversely affects the accumulation response.
EP 1 073 123 A2 (Yasuhara) describes a lateral power MOSFET which has a plurality of auxiliary electrodes arranged in a drift zone of the component and isolated from the drift zone by a dielectric. These auxiliary electrodes are composed of a semi-insulating polysilicon (SIPOS), a resistance material, and are connected between a source connection and a drain connection of the component. The auxiliary electrodes result in the formation of a depletion zone (depletion layer) in the drift zone when the component is driven in the blocking state.
GB 2 089 118 A describes a power MOSFET which has a resistance layer which extends along the drift zone between a gate electrode and a drain electrode and “spreads” an electric field in the drift zone, with the aim of increasing the withstand voltage.
U.S. Pat. No. 5,844,272 (Söderbärg) describes a lateral radio-frequency transistor with a drift zone running in the lateral direction of a semiconductor body and with a further semiconductor zone which is arranged adjacent to the drift zone above the semiconductor body and is isolated from the drift zone by an isolation layer. This further semiconductor zone is connected to the drain zone via a diode and results in the formation of an accumulation channel in the drift zone along the isolation layer when the component is in the on state.
US 2003/0073287 A1 (Kocon) proposes that a plurality of field electrodes, which are at different potentials, be provided along the drift path. However, this is very complex to implement.
In the case of an IGBT (Insulated Gate Bipolar Transistor), the on-state resistance is reduced by flooding the drift part by means of additional injection of a second charge carrier type. However, this results in considerably higher switching losses since these additional charge carriers must be removed again when the component is switched off.
The object of the present invention is to provide a semiconductor component, in particular a power semiconductor component, with a drift path, which component has a low on-state resistance and in which the disadvantages mentioned above do not occur.